The alleged terrorist group, Ansar al-Muslimeen -- more commonly known as Ansaru -- released video stills claiming they contained photos of some of the bodies. According to CNN, the group blamed the deaths on a joint Nigerian-British military effort to free the hostages.
The Nigerian authorities on Sunday told Reuters that they had no information about the deaths.
However, a statement from the Italian Foreign Ministry countered that statement: "Our checks conducted in co-ordination with the other countries concerned lead us to believe that the news of the killing of the hostages seized last month is true."
The Greek Foreign Ministry also confirmed to Reuters the death of the Greek citizen.
IBTimes has not yet been able to independently verify the reports. Updates will be posted here.